Phase change inkjet printers receive phase change ink in a solid form and then melt the solid ink to produce liquid ink that is used to form images on print media. Phase change inkjet printers form images using either a direct or an offset (sometimes called indirect) print process. In a direct print process, melted ink is jetted directly onto print media to form images. In an offset print process, melted ink is jetted onto a surface of a rotating member, such as the surface of a rotating drum, belt, or band. Print media are moved proximate the surface of the rotating member in synchronization with the ink images formed on the surface. The print media are then pressed against the surface of the rotating member as the media passes through a nip formed between the rotating member and a transfix roller. The ink images are transferred and affixed to the print media by the pressure in the nip.
Offset phase change inkjet printers utilize drum maintenance units (DMUs) to facilitate the transfer of ink images to the print media. A DMU is usually equipped with a reservoir that contains a fixed supply of release agent (e.g., silicon oil), and an applicator for delivering the release agent from the reservoir to the surface of the rotating member. One or more elastomeric metering blades are also used to meter the release agent on the transfer surface at a desired thickness and to divert excess release agent and un-transferred ink pixels to a reclaim area of the drum maintenance system. The collected release agent is filtered and returned to the reservoir for reuse.
DMUs are typically provided in a modular form capable of being installed and removed from an imaging device as a self-contained functional unit. The fixed supply of release agent in a DMU provides adequate oil for image transfer for a limited number of prints depending on an average oil usage per print and the quantity of the oil in the reservoir. When the supply of release agent has been depleted, the DMU is removed and replaced with a DMU having a fresh supply of release agent. Replacing DMUs as they are depleted of release agent adds to the operating cost of an imaging device. Finding ways to reduce the amount of oil that is removed from a DMU over time can increase the useful life of the DMU and thus decrease the cost of operating an imaging device.